Dogs are bitten mainly around the nose. You would certainly see the bite there as adder venom contains anti coagulants and it will bleed if envenomation has taken place, it will also start swelling considerably and the dog will obviously feel the effects and you will see that behaviour very clearly. Adder venom is quite a powerful cocktail. A compression bandage won't be much use around that area, and don't waste time if it was bitten on a limb, just pick it up and get to a vets. No point in taking a picture as the adder is our only venomous snake and it will disappear quickly once the dog has retreated anyway. Diagnosis of snake bite is quite easy, it is unmistakable compared to the much lesser effects of an insect sting and the effects are immediate.
Dogs have a remarkable system to aid recovery from adder bites, but even so, fatalities occur every year due to vets that diagnose incorrectly, and owners that don't take action. Recovery is not a certainty, but the adders reluctance to inject a full dose, the owners swift response, and the vets actions, make survival a very high probability. The best course of action is to find a local vet who is equipped to deal with a bite now, then you have all bases covered if a bite does occur. Just remember that even with nosy boisterous dogs, the adder will get away without incident 99% of the time. It requires a snake cornered without retreat to bite, which is rare. So even if your dog does encounter one, it is unlikely to receive a bite. Just locate a vet you know that can deal with the situation now, and your dog will be good, even if the worst happens. Just try to avoid those areas around March, April and into early May, as this is the breeding season, and male adders lose their timidness as they search out mates and spend more time in the open.